This invention relates to an automated materials processing furnace that is capable of high temperature operation. In particular, this invention enables the processing of material samples under both terrestrial and microgravity conditions and provides for the monitoring of process parameters.
The ability to more accurately predict and/or control the behavior of materials processed at high temperatures allows researchers and industry to develop commercial processing conditions which optimize the manufacture of these materials. Such processes involve areas that deal with:
Coefficients of liquid diffusion
High temperature semiconductor crystal growth
High efficiency infra-red glass processing
Travelling liquid-solid interface characterization
The information attained from current terrestrial experiments involved in such investigations, have generated wide and varying results. The primary source of these variations is the effect of convection at high temperatures when the material is in a liquid state. The removal of convective influences provides a significantly improved determination of the underlying processing characteristics. This can be attained through the reduction of gravity.
Earth bound xe2x80x9cnear-zeroxe2x80x9d gravity (xcexcg) can be attained for short intervals of up to 25 seconds. However, these high temperature processes normally require extended periods of xcexcg in order to complete a particular investigation. Currently, the only viable environment capable of attaining these conditions is the NASA Space Shuttle and the International Space Station (ISS). Unfortunately, the design and operation of any hardware on the Space Shuttle or ISS are restricted by standard predefined safety criteria, physical size, power consumption and available crew time.
The safety criteria imposed by NASA on a particular flight qualified payload (facility) is directly related to the standard set of design specifications established to protect the crew and the Space Shuttle systems. Of these, the most applicable to materials processing facilities are:
Containment of toxic and/or molten specimen materials
Limitation of surface touch temperatures to below 49xc2x0 C.
Control of electromagnetic interference
The size restriction is related to the need to conform to the standard payload dimensions specified for locating and mounting hardware to the Shuttle or ISS structure. The two types of standard units are a locker and a rack.
Power consumption limitations are a capacity limit for the Shuttle and ISS. A payload has a maximum allocated energy consumption per day that has a specified peak and average power limit. It is therefore desirable to design the payload for operation at the lowest possible power level since this will allow longer daily operations.
Crew time restrictions are imposed by NASA in that experiments are allocated a certain amount of weekly crew time. Since initiating the construction of the ISS in 1998, the time allocations of the crew for the operation of experiments on the Shuttle is becoming more restricted and it is predicted that it will be even more so on the ISS. Facility space is always at a premium since there is limited working space on both the Shuttle and the ISS. These restrictions indicate that for a payload to be productive in this environment, the design needs to maximize the utility of the available working space and to include components that minimize the crew time associated with conducting the experiment.
Previous designs for high temperature experimental hardware have generally been single function furnaces that required a significant amount of crew time to support the operation. One such facility is the QUELD furnace which flew in 1992. This was a single zone furnace that was designed for the processing of samples for liquid metal diffusion studies. The unit""s performance allowed for the isothermal processing of materials at temperatures up to 940xc2x0 C. The unit required significant astronaut intervention for process initiation, sample insertion, sample removal and quenching. The system also required the sample to move with respect to the furnace which could cause unwanted disturbances of the specimen material prior to sample cooling. As the furnace relied on astronaut interventions for processing the samples, there was a risk that the samples were not processed correctly. The requirement for astronaut interventions also limited the number of samples that could be processed based on the available crew time.
Another single function facility is the CFZF facility which is a float/travelling zone facility that utilizes focused movable halogen lamps to create a molten zone in a sample. The furnace accomplishes a travelling melt zone by slowly moving the lamp focal point along the length of the sample. The CFZF is configured only as a float zone furnace and processes one sample before requiring sample replacement by an astronaut. Manual sample insertion by an astronaut runs the risk of potential error in sample installation resulting in incorrect processing. Astronaut time limitations also restrict the number of samples that can be processed.
The AGHF facility is a Bridgeman furnace used as a single processing mode furnace for directional solidification and crystal growth. The system uses a mobile liquid cooling ring to create a moving temperature gradient. The AGHF is operated as a gradient furnace and utilizes one sample per process run and requires astronaut intervention for sample replacement. The risks for astronaut error are again present during the sample installation and the available crew time limits the number of samples in a given mission.
Another facility that was designed for use in limited studies is the LIF facility which is a single zone isothermal furnace capable of processing materials to 1600xc2x0 C. The unit uses only a single sample and requires astronaut intervention for replacement. This limits the number of samples that can be processed and is also prone to astronaut error in operator procedures. The LIF employs an internal limited capacity helium gas cooling system for the sample which also limits the number of samples that can be processed.
The AADSF is another directional solidification furnace that achieves a moving temperature gradient across the sample by moving the sample over a stationary heating zone. The motion of the sample over the heating element during processing may induce unwanted vibrations in the specimen material.
The TEMPUS facility uses a degree of automation to reduce crew time but still has limitations with respect to scientific versatility. The TEMPUS is an electromagnetic levitation furnace that employs the heating of spherical samples using radio waves. The sample is stabilized in the middle of a magnetic field while the material is processed. The TEMPUS has a capacity of 22 samples contained in a carousel that automatically rotates each sample into position for processing. The unit is limited to those materials that can be contained in a magnetic field, heated by radio waves and have a sufficiently low vapour pressure when molten so as not to contaminate the processing vessel. The unit also provides only simple uniform heating.
The QUELD II facility attempted to address the design issues of process flexibility and reduced crew time. The facility is a 3 zone multi-purpose facility that was initially designed to be used on the MIR space station for processing several different types of materials (liquid metals, semiconductors and infra-red glasses) during a two year period. The sample automation of the unit was limited to two samples per astronaut intervention. There was also the requirement for the astronaut to input into the facility the correct process program number and therefore was prone to processing error. The processing of the samples involved a stationary furnace and movable samples and again the movement of the sample from the furnace to the cooling quench blocks could cause unwanted disturbances in the specimen material. The unit was also limited to the processing of materials below 900xc2x0 C. with a gradient temperature performance dependent on the thermal conductivity of the sample. The entire unit was not designed to be installed in a standard locker configuration as it was to be operated in conjunction with the microgravity isolation mount (MIM) and does not conform to the mechanical and electrical connections of a Shuttle or ISS locker.
Limitations and restrictions on available resources, crew time in particular, on the Shuttle and the ISS are key considerations in any design for a high temperature materials processing facility. The optimization of the available space is crucial to maximise the potential science return on a per flight basis as the flight opportunities are rare and expensive.
There is therefore an important need to develop hardware that processes materials using a movable high temperature furnace that is designed to maximize the processing capabilities in order to support multiple types of research. It is also important that the design utilizes stationary multiple samples that minimize disturbances to the specimens, maximizes the number of material samples to be contained in the space, and minimizes the required crew intervention time. Furthermore, it is desirable for the process parameters for each sample to be automatically defined upon installation of the samples, thereby minimizing potential crew errors.
We have designed in accordance with the present invention, a system that provides for the high temperature processing of materials which utilizes a movable furnace that enables the selection of stationary samples mounted in an array to be inserted into either end of the furnace.
According to a further aspect of the present invention, the movable furnace contains two or more independently controlled thermal regions, each containing one or more heating elements, that allow for differing thermal profiles over the sample.
According to a further aspect of the present invention, the sample insertion is achieved by the movement of the furnace along its primary axis such that the stationary sample becomes inserted within the furnace.
The materials processing furnace contains one or more replaceable sample arrays each containing one or more stationary samples which are processed automatically according to predefined conditions. Periodic intervention by an operator can be used to replace the sample array and collect associated data.
According to a further aspect of the present invention, a sample is attached to the sample array via mechanical couplings that control the thermal union between the sample and array. The couplings are composed of materials that allow the thermal union between the sample and array to be thermally insulative or conductive.
The materials processing furnace contains one or more movable quench block assemblies that cool the stationary sample from a high temperature by the movement and subsequent contact of quench blocks on to the sample.
According to a further aspect of the present invention, the quench blocks are composed of a series of segmented sections that self adjust to the exterior profile of the sample and remove heat via passive heat sinks or active heat transfer devices.
The materials processing furnace may be operated in microgravity in order to eliminate the scientifically disruptive effects of convection.
According to a further aspect of the present invention, the microgravity condition is provided by operation in an interface shell that is used in a Shuttle or ISS locker and can be used in combination with an active microgravity isolation platform to minimize external vibration disturbances.
The materials processing furnace contains one or more protective layers of physical containment in order to meet the safety requirements of high temperature processing in microgravity conditions.
According to a further aspect of the present invention, the physical containment can be provided entirely by the sample or by the furnace or a combination of both.
According to a further aspect of the present invention, physical manipulation of the material specimen is accomplished though external stimulation, used singly or in combination, and consisting of magnetic, electrical or thermal devices that do not compromise the integrity of any protective layers of physical containment.
The materials processing facility may be configured to accommodate one or more materials processing furnaces as interchangeable units. Each of the interchangeable units contains electronic modules to control the operation of the furnace, and the interchangeable units connect with a base unit that provides for mechanical and electronic attachment. The base unit contains one or more electronic modules that allow for the remote control and operation of the furnaces.
According to a further aspect of the present invention, the interchangeable units may incorporate a touch screen display to enable monitoring and adjustment of the processing facility.
The utility of the present invention has significant advantages associated with microgravity material investigations, it is also foreseen that there will be considerable terrestrial application of the present invention for experimentation in a terrestrial laboratory in preparation for flight and for regular experimental use.